Effect of reinforcement particle size on microstructure and impact toughness of iron-matrix composites

This work used 5CrMnMo steel and titanium carbide (TiC) powders to fabricate particulate metal matrix composites (PMMCS). The composites’ microstructure, microhardness, and impact toughness were compared with four different titanium carbide ceramic particle sizes. The phase composition and microstructure of composites were studied. Vickers hardness and Charpy impact tests were employed to analyze composites’ microhardness and impact ductility, respectively. The results showed that the four groups of composites are mainly composed of martensite, trace residual austenite, and titanium carbide (undissolved TiC and primary TiC particles). With the growth of the ceramic particle dimension in the composite layer, the number of primary titanium carbide ceramics gradually decreased. When the initial ceramic particle size was small, it tended to generate dendritic primary TiC, and when the particle size was large, it tended to generate polygons and ellipsoids. Furthermore, with the growth of titanium carbide ceramic particle dimension in the composites, the microhardness of the composites decreased but the impact toughness of the composites rose first and then descended. When the ceramic particle size was 50 − 75 μm, the composite had the highest hardness, and the impact energy of the composites was the highest, which is 8J. This was because there were more undissolved titanium carbide ceramics in the composite, and there was a thicker matrix metal between the ceramic particles.